A method and apparatus for orienting binder-coated wood strands into parallelism has been described in pending U.S. application Ser. No. 535,079, filed Dec. 20, 1974 now U.S. Pat. No. 4,058,201. As described in this application, wood strands may be felted in a number of layers with the orientation of adjacent strand layers being generally perpendicular to each other. Thus, after compressing the mat of strand layers and curing the binder on the wood strands, a board is produced which has superior structural properties. Such a product is of the type described in U.S. Pat. No. 3,164,511.
U.S. application Ser. No. 535,079 further describes an apparatus comprised of a plurality of elongated, parallel, relatively thin plate-like strand guide members positioned above a moving support. The longitudinal axes of the guide members extend substantially parallel to the surface of the support, and the widths or the short axes of the guide members are substantially perpendicular to the surface of the support. The distance from one guide member to the next adjacent guide member is less than the lengths of the majority of the wood strands.
During operation of the apparatus, adjacent guide members move in opposite directions with respect to each other and in the general direction of their longitudinal axes. As the guide members move, wood strands are caused to gravitate from above the guide members. Moreover, each guide member has spaced projections on its upper margin which operate to turn those strands which, instead of immediately passing through the spaces between the guide members, are intercepted and span the distance between two or more guide members, such turning action continuing until the strands fall into the spaces between the guide members and onto the moving support therebelow. Using this method and apparatus, strands may be oriented parallel to the direction of movement of the support and perpendicular to the direction of such movement, depending upon the positions of the guide members relative to the direction of support movement.
The technology in the industry is available to produce wood strands of generally uniform length. Such strands can be oriented into parallelism at a high through-put rate with apparatus of the type described in U.S. application Ser. No. 535,079 using projections of the type described above on the upper margins of the guide members and with a spacing between each pair of adjacent guide members selected to accommodate strands of this uniform length. It is recognized, however, that to produce strands of uniform length would be costly and would not be economical for mass production of oriented strand boards.
If all wood strands were of relatively uniform length, the distance between the guide members could be a little less than one-half the maximum strand length to assure proper orientation. If the guide members used for orientation have upper marginal projections with generally vertical end edges, the apparatus would then achieve a relatively high through-put and the strands would not bend or break. If the distance between the guide members is considerably smaller than one-half the maximum strand length and such projections with vertical end edges are used, then the longer strands would span three or more guide members and be engaged by three or more such projections on the corresponding three or more guide members at the same time. This would result in a number of broken or bent strands and this number would increase with an increase in strand length or decrease in the distance between the adjacent guide members.
In view of the foregoing problems, a need has arisen to provide apparatus and method to orient wood strands having different, non-uniform lengths which are felted onto moving guide members simultaneously. The objective is to accommodate such wood strands of different lengths without breaking or bending the long strands yet still permitting the alignment of the short strands into parallelism while maintaining a relatively high through-put.